I. Technical Field
This invention pertains to actuators such as solenoids and/including but not limited to magnetic latching actuators.
II. Related Art and Other Considerations
Some actuators have a piston or plunger which is electromagnetically attracted by energization of a coil in an axial direction of the plunger to a base member enclosed within an actuator housing. The base member is, in turn, in contact or aligned in the axial direction with yet another member. Such other member can be, for example, an actuator end cap of the housing or (in the case of a latching actuator, for example) magnetic material that facilitates holding of the piston toward the base even after the coil has been de-energized.
The piston striking the base upon coil energization can produce noise, as can the struck base contacting (or transmitting the sound through) the member with which the base is axially aligned. Normal magnetic latch actuators have magnetic bases that are rigidly mounted to maximize latching forces. One adverse effect of this design approach is very high audible noise levels which can occur when the magnetic base is struck by a reciprocating member, such as a plunger or piston of the actuator. In some instances a solid or elastomeric material intended to serve as a noise dampener may be placed axially between the base and the axially aligned member.
For example, FIG. 6 shows a magnetic latching solenoid comprising a plunger P that reciprocates through an opening in a solenoid end plate T. Upon energization of coil C the plunger is retracted into the solenoid frame F and strikes a base member B. An elastomer E is provided in an axial direction between base member B and frame F, and essentially serves as a cushion. A narrowed portion of base member B extends through frame F and has an enlarged riveted end R for retaining the base member B relative to frame F. Energization of coil C causes plunger P to travel toward and strike base member B, causing base member B to compress elastomer E and slightly drive riveted end axially. Because the riveted end R is magnetically attracted to frame F, the impact force of plunger P must exceed that magnetic attraction before elastomer E can start to compress. After de-energization of coil C, magnetic flux provided by magnet M, located at an opposite end of the solenoid from base member B, extends through the plunger P to hold plunger P in contact with base member B. The magnetic flux lines extend through the narrowed portion of base member B, resulting in higher flux density in the narrowed portion and thus causing more iron losses. The elastomer E is intended to provide some noise dampening when the plunger P strikes the base member B. However, the elastomer E is much stiffer in compression (in the axial direction) than in shear. Moreover, when the base member B returns to its original position, the enlarged riveted end R impacts frame F, thus causing an additional noise.